People love escapism. The seas also are terrifying like being buried alive in a way that dying of a spacecraft crash never will be.
it comes back to the opposing metaphors of "going up" and "going down". We bury the dead (and many secrets) beneath our feet, while moving up literally puts us in a position superior to our fellow man. Literally, if I climb a mountain, I'm hundreds of feet above everyone else. Wealthy people and rulers have for years lived on hills. It follows that our betters deserve an optimum vantage point where they can "oversee" our daily toiling. We are told the air is more pure the higher you go, whereas at sea level one is exposed to the filth and fumes emitted by common people.
drug metaphors have for years been awash in references to flight; enhanced or expanded consciousness has been equated with elevation. conscious existence is defined by the drug culture as existing on the earth's surface, to escape it requires a trip "up". if we recall the book of Jonah, the reluctant Jonah, at odds with God, encounters a great storm at sea, is tossed into the ocean, and is swallowed alive by a whale. subsequently, he pledges his devotion to God and the whale spews him out of the depths of the ocean onto dry land. there are painfully apparent psychological implications to the Jonah myth, but even more obvious is how the disobedient and angry man is thrown "down" into the black abyss where a giant monster swallows him. when he agrees to become good, he is thrown "up" and his life begins anew in service to God. the baptism ritual doesn't involve tossing a person into the air, does it?
why is heaven up in the sky and hell under our feet? why does just about everyone misinterpret the symbolism of the cross?
Ronnie James Dio seemed to get it:
"We're all born upon the cross
The throw before the toss
You can release yourself
But the only way you go is down."
I'm really glad Conservationist chose to lead the topic in the direction he did; there are a great many reasons why mankind obsesses over space flight while largely ignoring "undersea" exploration, and many of them have nothing whatsoever to do with colonizing Mars.